let _Vue = null

export default class VueRouter {
  static install (Vue) {
    // 1. 判断当前插件是否已经安装
    if (VueRouter.install.installed) {
      return
    }
    VueRouter.install.installed = true
    // 2. 把Vue构造函数记录到全局变量
    _Vue = Vue
    // 3. 把创建Vue实例时候传入的router对象注入到Vue实例上
    // _Vue.prototype.$router = this.$options.router // this指向当前函数
    // 混入
    _Vue.mixin({
      beforeCreate () {
        if (this.$options.router) {
          _Vue.prototype.$router = this.$options.router
        }
      }
    })
  }

  constructor (options) {
    this.options = options
    this.routeMap = {}
    let newHash = window.location.hash
    let path = ''
    if (newHash === '#/' || newHash === '') {
      path = '/'
      this.getHashUrl(this.options.base)
    } else {
      path = newHash.substr(1)
    }
    this.data = _Vue.observable({
      current: path
    })
    this.init()
  }

  init () {
    this.createRouteMap()
    this.initComponents(_Vue)
    this.initEvent()
  }

  getHashUrl (path) {
    let i = window.location.href.indexOf('#')
    window.location.replace(
      window.location.href.slice(0, i >= 0 ? i : 0) + '#' + path
    )
  }

  createRouteMap () {
    // 遍历所有的路由规则， 把路由规则解析成键值对的形式 存储到routeMap中
    this.options.routes.forEach(route => {
      this.routeMap[route.path] = route.component
    })
  }

  initComponents (Vue) {
    Vue.component('router-link', {
      props: {
        to: String
      },
      render (h) {
        return h('a', {
          attrs: {
            href: this.to
          },
          on: {
            click: this.clickHandler
          }
        }, [this.$slots.default])
      },
      methods: {
        clickHandler (e) {
          history.pushState({}, '', '#' + this.to)
          this.$router.data.current = this.to
          e.preventDefault()
        }
      }
    })

    const self = this
    Vue.component('router-view', {
      render (h) {
        const cm =   self.routeMap[self.data.current]
        return h(cm)
      }
    })
  }

  initEvent () {
    if (this.options.mode === 'hash') {
      window.addEventListener("hashchange", () => {
        let newHash = window.location.hash
        this.data.current = newHash.substr(1)
      });
    } else {
      window.addEventListener('popstate', () => {
        this.data.current = window.location.pathname
      })
    }
  }
}
